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This mechanism also works if the train enters and leaves the track section on the same
side
12.5 Prototypical Signalling
Almost each prototypical signalling system can be modelled by applying the Triggers
and Conditions (see page 181 and section 12.2) to signals. Beside Flagman elements
(see section 12.4) signals are another type of elements, to which these features can be
applied.
Especially by applying triggers to the particular states of a signal symbol, it is possible
to let this signal symbol respond to arbitrary situations with the display of an appropriate
aspect.
The following rules apply to the triggers of signals:
• The signal may change the displayed aspect, whenever an element changes its state,
that is contained in a trigger of one of the signal aspects.
• If the triggers of two signal aspects apply at the same time, then the software may
freely select one of these aspects.
• Empty triggers apply always. However when a non-empty trigger applies at the
same time, too, then the software selects the signal aspect associated with a nonempty
trigger. Non-empty triggers have got priority.
• Since non valid conditions may prevent a valid trigger from becoming effective (see
page 183) and a later change of the condition does not make up for the concerning
state change, a signal always reflects the situation at that moment, when one of the
triggers fired the last time; but it does not necessarily always reflect the current
situation.
According to the above the following recommendations apply:
• Specify the particular triggers assigned to the various aspects of the same signal in a
way, that no two different non-empty triggers become valid at the same time. Make
use of the NOT-option (see page 177) to exclude the triggers of other signal aspects
from a particular trigger.
• Leave the trigger of exactly one signal aspect empty, if possible. This is the “else”
case and specifies the signal aspect in all cases, where no trigger of another signal
aspect applies.
• To extend the simplified signalling system, which was introduced in section 5.9, and
which is based on a 1 to 1 mapping of the internally calculated block signal aspects,
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